Seems more like almost 2 meters to me at 100m. Last night, from the 3rd floor of the Grain Elevator, I was putting down people that were running parallel along the back wall with that amount of lead reliably. (About 117m max I think.) I dunno why but I visualized it as about a body length worth of lead and it was hitting more often than not.
Hmm... that seems excessive. Maybe the movement speed in game is faster than real life, but a man running directly across your field of view at 300m distance will need to be lead by 1.5 to 2m. So a body length lead at a full sprint directly sideways 300m target.
When I was taught to do it with the 5.56 Steyr AUG, the lead was calculated by aiming at the front, raised knee when at full stride. At 100m, if you aim at the knee when the thigh is horizontal, you will hit in the hip. If you take the length of the thigh bone and add that to the lead once, that is 200m. If you do it a second time it is 300m. Three thigh length lead is 300m.
What is good about this system is that you are using the target as the ruler and the reference point, so the size of the target (and therefore how much ground it can cover per step) is automatically scaled to range and orientation, and your aim point visibly moves with the target, making drop calculation easier. If he's not running straight across, the apparent length of the raised thigh will be shorter in direct relation to how much less sideways distance he will cover in the same time.
Even better is that you don't have to even try estimating how fast the target is running. The lead is calculated from the front knee which goes further forward the faster he is running, until it is horizontal at full stride and at full speed. So if you calculate the drop to hit the hips, but lead by the same distance the knee is in front of the body when it is at full stride, you will automatically give less lead to a man running slower than one running faster. You are using two reference points on the body to show you where to aim, rather than trying to guess.
You must watch the fall of shot and adjust your sights as accurately as possible though. If your sights are set too different, you also have to take account of that, which means guessing where to aim again. What I do is unless the target is clearly greater than 100m, I use the default setting of 100m and take an aimed shot as if that is exactly where the target is. Then I look to see if the bullet missed what it was supposed to hit - the hip - then assume this means he is at a different range. I trust my training in regards to lead and use it to help me calculate range.
So if the bullet hits at the height of his feet, regardless of if it is in front or behind, I assume he is further than 100m and change my sight to 200m and do it again. If the bullet flies high this time and goes over the height of his hips, regardless of horizontal offset, I now know he is somewhere between the two distances. If the first shot fell more below than the second flew above, I assume it's closer to the latter range, and so on.
Once I know I have the sight set the closest to his actual range, I will then use the knowledge gained (which side of the range and approximately how much) to estimate the offset I need to add to the visual lead calculated from the target. By your third or fourth shot you should only be trying to account for his movement between shots, rather than his movement in general, so it is like taking shots at several stationary targets.
If you are moving, be aware that you have to lead your own movement too. Also don't forget to treat groups of targets as a group. If you get a one shot kill on one, use that to narrow down the range for the others. You know how far away he was, so use that to act as a reference to estimate the other targets' range, and adjust your sights accordingly before beginning to shoot at the next target. You want to narrow down the variables in as few shots as possible, so every little bit of information about the target you can get, helps.
This works for the Steyr in the real world, but may not work here because of different flight times of the bullet. My experience in game has been that it works pretty well at all ranges I fire at, and I have had more than one running man kill at 200m+ with a three round burst from the DP-28 using this technique.
I've been messing arround the distance aim, and I can already know when to use the 100 or 200 one. And it does really make a difference, specially on Fallen Fighters. I've missed shots with the 100m aim, and after changing to the 200m one I one hit killed the targets instantly.